The present invention relates to point force sensors. More specifically, the present invention relates to point force sensors of sufficient sensitivity and accuracy for use in atomic force microscopes, strain gauges, surface measuring devices, miniature microphones, accelerometers, and similar low force sensors.
Highly sensitive point force sensors are necessary for a number of applications wherein the force between two points must be measured with great accuracy, such as when surface typography is measured in minute detail by an atomic force microscope on the subatomic scale. A number of atomic force microscopes are currently known, for example the oscillating quartz atomic force microscope taught in U.S. Pat. No. 4,851,671 to Pohl. In Pohl, a crystal is utilized to oscillate a tip which is brought into close proximity with the surface to be measured. The deviations in the oscillating frequency, as a result of the proximity between the tip and the surface, are utilized to calculate the surface typography. A number of other devices utilize a scanning tunnelling technique for measuring surface typography by bringing a biased tip into close proximity with the surface to be measured and then using a tunnelling current to measure the deflection of the bias mounting for the scanning tip. Atomic force microscopes of this type are taught in Gimzewski, et al.; U.S. Pat. No. 4,668,865; Binning, U.S. Pat. No. 4,724,318; Hansma, et al., U.S. Pat. No. 4,800,274; and Duerig, et al., U.S. Pat. No. 4,806,755.
While each of these microscopes can be utilized to sense the typography of a surface at a subatomic level, the techniques utilized for such measurement make it difficult to adjust and/or calibrate the devices. This difficulty is significantly increased when probes are replaced, and the optics required for replacement and proper adjustment are often complex. Adjustment is especially difficult when the instrument is operated in a high vacuum, since access to the instrument is prohibited.
Surface topography measurement on a rougher scale, can also be achieved by the device taught in U.S. Pat. No. 4,200,986 to Ackerman, et al., which utilizes a probe in contact with a surface to measure surface deviations of a machine part. The probe is connected to a strain gauge which is deflected as a result of deflections of the probe tip by deviations in the sensed surface.